The present invention relates to needlepunch nonwoven fabrics based on a blend of lyocell fibers and polyester fibers.
Over the years there have been many developments relating to the production of fibers and fabrics derived from cellulose and more particularly shaped cellulose articles such as fibers, yarns and fabrics. Industry has long sought to produce fabrics having properties which approach those of cotton fabrics because the latter are known for enjoying wide acceptance and preference among consumers.
The conventional process for making such materials as rayon is the viscose process which involves dissolving cellulose or a derivative of cellulose in a solvent, shaping the resulting solution and recovering the cellulose from the solution as a solid shaped article such as a fiber. The art has known about rayon for many years but there exist a number of significant disadvantages with rayon including its mechanical properties, poor wet collapse properties and a large increase in wet elongation even under low stress. More specifically, the wet modulus of conventional viscose reduces its applicability for many important functions where dimensional stability is needed.
Many efforts have been made to develop processes for making improved regenerated cellulose fibers having superior properties than the older rayon products with some success. For example, cellulose fibers have been made from a solution of cellulose in a tertiary amine N-oxide solution. This is disclosed, for example, by Graenacher et al., U.S. Pat. No. 2,179,181. However, there have been problems observed with the Graenacher system because of the low solids content which requires the handling of large volumes of solvents. Later developments include a system of dissolving cellulose in an anhydrous tertiary amine N-oxide; see Johnson, U.S. Pat. No. 3,447,939. Here again, however, large amounts of solvents are required to be handled.
Subsequent technology included the addition of different polymers dissolved in a solvent based on the tertiary amine N-oxide system; See Johnson, U.S. Pat. No. 3,508,941.
Further efforts have been devoted to producing cellulosic articles having properties more similar to those of cotton articles and more particularly having improved properties which enable the cellulose material to be used for a wider range of purpose. For example, McCorsley, U.S. Pat. No. 4,246,221 shows a process where cellulose is dissolved in a solvent containing a tertiary amine N-oxide and water which is a solvent for the cellulose. The solution is then shaped by extrusion or spinning first into air or other nonprecipitating medium to form a film or filament. Then the film or filament is stretched in the medium to impart improved physical properties prior to precipitation of the cellulose. Subsequently, it is treated with a nonsolvent which precipitates the cellulose. The shaped solution emerging from the shaping dye is pulled from its point of emergence from the dye at a speed faster than its emerging speed so that it is stretched and reduced in thickness in the space before the cellulose is precipitated in the nonsolvent. In this process, the technique of stretching is defined by the spin-stretch ratio which is the linear speed of the precipitated article divided by the linear speed of the solution emerging from the dye. Orientation of the cellulose molecules is achieved by the stretching in the solution and as a result develops the properties of the shaped article prior to precipitation of the cellulose. After precipitation of the cellulose, the properties are set. This eliminates the need for stretching after precipitation and avoids the need for drawing apparatus which conventionally was used in the past. Details of the process are disclosed in McCorsley, U.S. Pat. No. 4,246,221 which is relied on and incorporated herein by reference.
More recently, further improvements have been made in methods for producing this modified type of viscose cellulose, now called lyocell, including where the cellulose is suspended in an aqueous solution of the tertiary amine oxide containing water and is then heated to temperatures between 90 to 120.degree. C. with stirring. See Zikeli et al., U.S. Pat. No. 5,094,690. In that patent, the heat treatment is performed over a substantially shorter period of time in order to minimize the thermal load on the cellulose and the tertiary amine oxide. The system shown in Zikeli et al. utilizes a heating surface that spreads the solution of the cellulose and the tertiary amine oxide in layers of coats until the homogeneous solution of the cellulose has formed. Rapid heating is then feasible without degradation of the cellulosic material according to the patentees. Further details of the system for producing the modified cellulose are shown in Zikeli et al., U.S. Pat. No. 5,094,690 which is relied on and incorporated herein by reference.